This invention relates generally to golf balls, and more specifically, to a wound golf ball. In particular, this invention relates to a golf ball having at least a center, a cover and a wound layer having at least one thread. This invention is also directed to a golf ball where the golf ball has a high resilience for low swing speed players to increase flight distance.
Conventional golf balls can be divided into two general groups: solid balls or wound balls. The difference in play characteristics resulting from these different types of construction can be quite significant. Balls having a solid construction are popular with golfers because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a solid core, usually made of a cross linked rubber, enclosed by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents. In addition to one-piece solid cores, solid cores may also contain a number of outer layers,. such as in a dual core golf ball. The cover is generally an ionomeric material, such as SURLYN(copyright), which is a tradename for a family of ionomer resins produced by E.I. DuPont de Nemours and Co. of Wilmington, Del. Covers are typically a single layer but may also include one or more layers, such as in a double cover having an inner and outer cover layer.
The combination of the solid core and ionomeric cover materials provide a ball that is very durable and abrasion resistant. Further, such a combination tends to impart a high initial velocity to the ball, which results in increased distance. Because these materials are very rigid, however, solid balls can have a hard xe2x80x9cfeelxe2x80x9d when struck with a club. Likewise, due to their construction, these balls tend to have a relatively low spin rate, which can provide greater distance and increases accuracy off the tee.
At the present time, wound golf balls are preferred by some golfers for the spin and feel characteristics afforded by such a construction. Wound balls typically have either a spherical solid rubber or liquid center, around which many yards of a tensioned elastomeric thread are wound. The wound core is then covered with a durable cover material, such as SURLYN(copyright) or similar material, or a softer cover material, such as balata or polyurethane. Wound balls are generally softer and provide more spin, which enable a skilled golfer to have more control over the ball""s flight and landing position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enable the golfer to stop the ball very near its landing position.
Regardless of the form of the ball, players generally seek a golf ball that maximizes total game performance. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with a wide variety of performance characteristics to meet the players individual requirements. Thus, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers of all skill levels.
To make wound golf balls, manufacturers use winding machines to stretch the elastic threads to various degrees of elongation during the winding process without subjecting the threads to unnecessary incidents of breakage. Generally, as the elongation and the winding tension increases, the compression and initial velocity of the ball increases. Thus, a more resilient wound ball is produced, which is desirable.
For wound golf balls, the thread is typically formed by a calendar and slitting method rather than an extrusion method. The calendared thread typically has a rectangular cross-section, while extruded thread generally has a circular cross-section.
A number of different windings have been disclosed for use in golf balls. U.S. Pat. No. 4,473,229 to Kloppenburg et al. discloses a golf ball having a core formed of graphite fibers and windings made of graphite filaments and resins. Yarns are made with the graphite filaments and resins, and as many as four or more yarns are combined to form a final yarn used for winding. U.S. Pat. No. 5,713,801 to Aoyama discloses use of a layer of high tensile elastic modulus fibers wound about the core. The fibers have a tensile elastic modulus of at least 10,000 ksi (10,000,000 psi). Also, U.S. Pat. No. 5,816,939 to Hamada et al. discloses a rubber thread for winding with a tensile strength retention of at least 70%, a hysteresis loss of no more than 50%, and an elongation of 900 to 1400%.
Prior art wound golf balls and cores typically use polyisoprene rubber thread. The polyisoprene thread is wound onto the cores at elongations between 500 to 1000%. The amount of thread required for a golf ball core is dependent on the elastic modulus of the thread in the elongated state. Elongated polyisoprene thread generally has an elastic modulus of 10,000 psi to 20,000 psi. Further, the properties, in particular resilience, of the wound ball or core are dependent on how well the thread packs during winding. The dimensions of the thread and winding pattern control the packing density. Present art polyisoprene threads are typically at least {fraction (1/16)} inches wide by 0.02 inches thick, measured prior to winding. However, present art polyisoprene thread is commonly produced in thicknesses between 0.014 inches and 0.024.
U.S. application Ser. No. 09/266,847, filed Mar. 12, 1999, discloses a thread for winding having at least about 10 individual strands that are each at most about 0.01 inches in diameter. Preferably, the thread has more than 25 strands with diameters of less than about 0.002 inches. The smaller thread dimension allows the thread to be wound more densely. Preferably, the elastic modulus of the thread is greater than 20 ksi when wound about a center. Preferably, the maximum elongation of the thread is greater than about 8%.
It is thus desired to prepare golf balls having an improved wound construction to create a ball that achieves improved characteristics for low swing speed players.
The present invention is directed to a wound golf ball with high resilience for low swing speed players to give them greater distance off the tee while conforming to the USGA golf rules. Methods for measuring the resiliency of golf balls are well known by those of ordinary skill in the art. One method of measuring the resiliency of a ball at impact is to utilize an air cannon or other means of propelling a ball at velocities equivalent to those of a golf club head. The balls are fired at a massive rigid block, with the inbound and outbound velocities being measured. The velocity may be measured by the use of light screens, which measure the time required for the ball to travel a fixed distance. The fixed distance divided by the transit time is equivalent to the average velocity of the ball over the fixed distance. The ratio of the outbound velocity to the inbound velocity is commonly referred to as the coefficient of restitution (xe2x80x9cCORxe2x80x9d). The COR is a direct measure of the resilience of a golf ball at a particular inbound velocity. Since golf balls behave in a linear-viscoelastic fashion, inbound ball velocity is functionally equivalent to club swing speed. The present invention seeks to maximize the COR for low swing speed players. These players swing the club at the ball with low swing speeds, and thus tend to obtain lower ball velocity after impact and less distance off the tee.
The golf ball according to the present invention includes a wound golf ball comprised of a center, a cover and a layer of windings disposed between the center and the cover. The center of the golf ball may be solid or liquid filled. Preferably, the center is solid. In one embodiment, the golf ball has at least one intermediate layer disposed between the center and the cover, i.e., one or more additional layers on either side of the layer of windings can be included in the golf ball. In another embodiment, the center itself includes more than one layer. The golf ball is wound with at least one thread, and a cover is preferably placed over the windings. Preferably, the center is at least about 1.1 inches. Most preferably, the outer diameter of the center is about 1.2 to 1.5 inches. Preferably, the combination of center and the wound layer has an outer diameter of about 1.4 to 1.63 inches. Thus the wound layer is thin in this embodiment.
In one embodiment, the cover material has at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi, and the golf ball has a compression from about 50 to 120.
The golf balls according to the present invention are tested by measuring COR as discussed above by launching the golf balls at velocities of 110 ft/s and 160 ft/s+/xe2x88x920.5 ft/s. Most preferably, the wound golf balls according to the invention have a COR, at 160 ft/s, greater than or equal to 0.76 and a gradient of the COR of at least about 0.001 s/ft, thus resulting in a large increase in resilience as the club swing speed decreases.
The threads may be formed of a suitable material including polyisoprene. Suitable polymers include polyether urea, such as LYCRA(copyright); polyester urea; polyester block copolymers, such as HYTREL(copyright); isotactic-poly(propylene); polyethylene; polyamide; poly(oxymethylene); polyketon; poly(ethylene terephthalate), such as DACRON(copyright); poly(p-phenylene terephthalamide), such as KEVLAR(copyright); poly(acrylonitrile), such as ORLON(copyright); diaminodicyclohexylmethane; and dodecanedicarboxylic acid, such as QUINA(copyright); or combinations thereof. LYCRA(copyright), HYTREL(copyright), DACRON(copyright), KEVLAR(copyright), ORLON(copyright), and QUINA(copyright) are available from E.I. DuPont de Nemours and Co. of Wilmington, Del. Glass fiber and, for example, S-GLASS(copyright) from Corning Corporation of New York can be included as suitable thread material. Also, D7 Globe thread by Globe Manufacturing of Fall River, Mass. can be included. Most preferably, the golf ball is wound with a polyether urea thread, such as LYCRA(copyright). Preferably, these threads contain at least about 10, more preferably at least about 100 strands. Each strand diameter is on the order of less than about 0.0001 inches. For optimal resilience, the polyether urea thread is elongated from about 200 to 500% to produce threads that are wound and densely wrapped.
The inner sphere, or center, of the golf ball is made of a composition, such as a thermoset solid rubber sphere, a thermoplastic solid sphere, wood, cork, metal, or any other suitable material known or available to one of ordinary skill in the art, or any combinations thereof, such as a rubber/metal multi-layer center. Preferably, the solid inner sphere is formed of a material that includes a resilient polymer such as polybutadiene, natural rubber, polyisoprene, styrene-butadiene, or styrene-propylene-diene rubber. In one embodiment, the center can include more than one layer. Similarly the inner sphere could be a liquid filled sphere or shell such as a rubber sack, a thermoplastic, or metallic shell design, in which the liquid could be of any composition or viscosity. It is also feasible to construct such a center with a void or gas center. In another embodiment, the center can be filled with a liquid, a gel, a paste, a cellular foam, or a gas.
Finally, a cover is molded around the core. The cover can also have one or more layers. Any process that results in accurate and repeatable central placement of the core within the cover is acceptable and preferred. Generally, covers are applied by compression molding, injection molding or casting cover material over the core. In one embodiment, the golf ball weighs less than about 45.93 g, preferably less than about 44 g, and more preferably less than about 42 g. In another embodiment, the golf ball weighs from about 40 g to 44 g, preferably from about 42 g to 44 g.
In one optional embodiment, the invention relates to the golf ball wherein at least one of the center, the cover, or the wound layer includes a material formed from the conversion reaction of an amount of polybutadiene, a free radical source, and a cis-to-trans catalyst, which reaction occurs at a sufficient temperature to form a polybutadiene reaction product which includes an amount of trans-polybutadiene greater than the amount of trans-polybutadiene present before the conversion reaction. In one embodiment, the reaction product has a first dynamic stiffness measured at xe2x88x9250xc2x0 C. that is less than about 130 percent of a second dynamic stiffness measured at 0xc2x0 C. The cis-to-trans catalyst preferably includes at least one of a Group VIA element, an inorganic sulfide, an aromatic organic compound, an organosulfur component, or a combination thereof. The cis-to-trans catalyst is typically present in an amount from about 0.01 to 25 parts per hundred of polybutadiene. In one embodiment, the reaction product is disposed in at least a portion of the center or the wound layer. In yet another embodiment, the thread material is tensioned and includes the reaction product. Also included are methods for forming a portion of the golf ball by combining (a) a cis-to-trans catalyst; (b) a free radical source; and (c) a first resilient polymer component including a cis-polybutadiene component present in an amount greater than about 70 percent of the total polymer component, converting a portion of the first resilient polymer component to a second resilient polymer component in about 5 to 18 minutes at a sufficient temperature to convert at least a portion of the cis-polybutadiene component to a trans-polybutadiene component and wherein the polybutadiene in the second resilient polymer component is at least about 10 percent trans-polybutadiene and less than about 7 percent vinyl-polybutadiene, and forming the second resilient polymer component into at least a portion of the center, the wound layer, or the cover of the golf ball.